The Integumentary
System of Invertebrates
The integument is the external
covering of n animal.
Integument of Protozoa
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Plasma
membrane is the only integument of single-
celled protozoa. This has large
surface which helps in gas exchange,
removal of wastes and also in absorption of dissolved nutrients from
surrounding fluid.
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Pellicle
(thick protein coat) is a semi-rigid structure which is present outside the
plasma membrane is the integument of paramecium.
Movement of entire body of protozoa occurs as pellicle transmits the force of
cilia or flagella to entire body.
Integument of Multi-cellular Invertebrates
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Single layer of columnar epithelium is present
in them and forms outer layer called epidermis. This layer lies on basement
membrane. Cilia are present on the
epidermal cells of the outer surface. Glandular
cells are also present on the epidermis of some invertebrates which helps
in the secretion of non-cellular material.
Integument of Cnidarians
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In hydra,
few cells thick epidermis is present.
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In corals,
shell is present that is composed of calcium
carbonate secreted by mucous glands.
Integument of Platyhelminthus
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Tegument
is the complex syncytium which is the outer covering of the tapeworms and parasites flukes. This
tegument helps in protection against digestion by host enzymes and in nutrient
ingestion.
Integument of Aschelminthus and Annelids
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One-celled thick epidermis is present in them
and multicellular cuticle is
secreted by it.
Integument of Echinoderms
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Thin ciliated epidermis is present in them and
connective tissue dermis is present under it which contains calcium carbonate.
Integument of Arthropods
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In crustaceans,
insects, and arachnids, thick
and rigid cuticle is present that supports the body. Chitin and rigid plates
are present in such cuticle and linked by flexible membrane.
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In rotifers,
cuticle is thin and elastic.
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There is one disadvantage of cuticle because
animals face difficulty in growing.
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Ecdysis
is the process by which insects shed old cuticle and replaced it with new one.
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In insects, exoskeleton
is also present.
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